1. Field of the Invention
This invention relates to a selective etching method, an optoelectronic device and its fabricating method suitable for use in, for example, a semiconductor laser using a II-VI compound semiconductor.
2. Description of the Prior Art
In recent years, demand for semiconductor lasers capable of emitting light of short wavelengths has increased for improving the recording density of optical discs and resolution of laser printers, and vigorous studies have been done with the aim of realizing it.
The present Applicant, after earnest studies to meet such demand, already proposed a semiconductor laser using ZnMgSSe compound semiconductors as materials of cladding layers and other layers and capable of emitting blue to green light (for example, Japanese Patent Application No. Hei 4-229356) corresponding to U.S. Ser. No. 101,725, filed Aug. 4, 1993.
The above-mentioned semiconductor laser using ZnMgSSe compound semiconductors, in general, additionally includes one or more materials such as ZnSe compound semiconductors other than ZnMgSSe compound semiconductors. When fabricating the semiconductor laser, selective etching may be needed to process the ZnSe compound semiconductor provided on a ZnMgSSe compound semiconductor layer into a mesa-type or other type pattern.
A method for etching the ZnSe compound semiconductor layer is a wet etching method using a K.sub.2 Cr.sub.2 O.sub.7 : H.sub.2 SO.sub.4 etchant. In the wet etching method, however, the etching rate of the ZnMgSSe compound semiconductor layer is faster than the etching rate of the ZnSe compound semiconductor layer, which results in the underlying ZnMgSSe compound semiconductor layer being deeply etched during etching of the ZnSe compound semiconductor layer thereon.
Means heretofore available for preventing this problem is a method of estimating etching time required for etching the ZnSe compound semiconductor layer on the basis of the etching rate of the ZnSe compound semiconductor to control the etching depth in view of the estimated etching time. This method, however, involves a problem from the viewpoint of controllability and reproducibility.